This invention relates to a cholesteric liquid crystal display device, and, more particularly, to a cholesteric liquid crystal display device employing an internal mask and back opaque layer to provide higher quality images.
A typical cholesteric liquid crystal display device comprises a cholesteric liquid crystal material disposed between two transparent plates. The inner surface of each plate is coated with a transparent, conductive film which serves as an electrode. In response to an electric field applied between the electrodes, the cholesteric liquid crystal switches between a transparent state and a reflective state. Typically, the electrodes are patterned such that the portions of the cholesteric liquid crystal they activate electrically will form an image.
The liquid crystal immediately adjacent to the activated liquid crystal may also become activated, resulting in a "bleeding" of the image into the area surrounding the desired image. This results in a fuzzier, lower-quality image. In addition, once cholesteric liquid crystal material is activated, it remains activated. While this provides a benefit over other liquid crystals in that there is no need to repeatedly redraw the image, this characteristic of cholesteric liquid crystals may also negatively effect image quality. Because cholesteric liquid crystals can be activated by temperature and flexion stresses, not just electrically, areas of the display may be activated which were not intended to be activated. Once activated, the unwanted display areas cannot be readily deactivated. This results in unnecessary image elements in the display and lower quality display images.
Thus, there exists a need for a cholesteric liquid crystal display device that forms a predetermined image having improved image quality and contrast, and without image detraction due to activation of unwanted regions.